Schematic / Layout

Stromversorgung

The board takes fixed 5V input, (with the 1V2 core voltage generated directly from the input using the internal switch-mode supply on the BCM2835 die).
This permits adoption of the micro USB form factor, which, in turn, prevents the user from inadvertently plugging in out-of-range power inputs; that would be dangerous, since the 5V would go straight to HDMI and output USB ports, even though the problem should be mitigated by some protections applied to the input power: The board provides a polarity protection diode, a voltage clamp, and a self-resetting semiconductor fuse.

Board A: 5V, 500 mA (2.5W) without any devices connected

Board B: 5V, 700 mA (3.5W) without any devices connected

As the 5V rail is brought out in the GPIO pins, you can power the Rpi from there too. You should mind however, that those are behind the power protection circuitry , so you should provide your own.

It is possible to power the Rpi from a powered USB hub the Rpi controls, but only on 'dumb' devices, that allow the port to supply the full current without waiting for the usb device to ask for it[1]. As the power input of the Rpi doesn't have its data leads connected, there is no chance for a communication loop of some sorts.

POE (power over ethernet) is currently not available for the Rpi (but nobody stops you from taking your soldering iron and doing it yourself)